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Ape evolution Our ancestors made the evolutionary split with gorillas around 10 million years ago, but we still share a remarkable number of genes with the great ape, a new study shows.

A worldwide consortium of scientists sequenced the genome of the western lowland gorilla and compared more than 11,000 of its key genes with those of modern humans, Homo sapiens, and chimpanzees.

Gorillas diverged from the human-chimp lineage around 10 million years ago, and around four million years later, H. sapiens and chimps emerged on their own as a separate species, a figure that tallies with fossil evidence.

The comparison also overturns convictions about similarities between the major primates, the researchers report in the latest issue of Nature .

As expected, humans and chimps shared the most genes, they found.

But 15 per cent of the human genome is closer to the gorilla genome than it is to the chimpanzee, and 15 percent of the chimp genome is closer to the gorilla genome than it is to human.

"Our most significant findings reveal not only differences between the species reflecting millions of years of evolutionary divergence, but also similarities in parallel changes over time since their common ancestor," says Chris Tyler-Smith from the Wellcome Trust Sanger Institute in the United Kingdom.

"We found that gorillas share many parallel genetic changes with humans, including the evolution of our hearing.

"Scientists had suggested that the rapid evolution of human hearing genes was linked to the evolution of language. Our results cast doubt on this, as hearing genes have evolved in gorillas at a similar rate to those in humans," says Tyler-Smith.

Gene flow

Gorillas themselves began to split into two groups, the eastern lowland gorilla and the western lowland gorilla, about a million years ago.

The study throws cold water over the notion that when primate species diverged, this happened rather abruptly, over a relatively short period. Instead, the process was longer and very gradual.

There was probably a fair amount of "gene flow," or inter-breeding between slightly different genetic strains, both before gorillas split from the other apes and before gorillas themselves diverged into two species.

There could well be a parallel in the split between chimps and bonobos, or between modern humans and Neanderthals, say the researchers.

The DNA sample came from a female western lowland gorilla named Kamilah.

After thriving for millions of years, gorillas survive today in just a few isolated, badly endangered populations in central Africa, their numbers diminished by hunting and habitat loss.

"As well as teaching us about human evolution, the study of the great apes connects us to a time when our existence was more tenuous, and in doing so, highlights the importance of protecting and conserving these remarkable species," say the researchers.